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From: Florian Weimer <fw@deneb.enyo.de>
Newsgroups: comp.lang.ada
Subject: Re: Preventing type extensions
Date: Mon, 13 Sep 2010 20:32:13 +0200
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Date: 2010-09-13T20:32:13+02:00
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* Dmitry A. Kazakov:

>> Type extensions break encapsulation (at least if there non-abstract
>> dispatching subprograms which contain some non-trivial code): the
>> information which subprograms call each other under what circumstances
>> leaks to the outside of the package. One very drastic way to
>> implement that is to disallow type extensions for most non-abstract
>> types you write, and consider the exceptions carefully.
>
> No, the actual problem here is re-dispatch. Just do not do that, it is
> always bad.

How do you suggest to avoid redispatch?  Make non-dispatching calls to
dispatching subprograms?  And how does this address the issue?

It makes it more likely that you cannot write a useful extension.
Wouldn't it be better not to hide this aspect in the implementation?